The present invention relates to a fuel cell system and to a method for judging fuel gas leak in a fuel cell system. More particularly, the present invention relates to an improved technology for detecting and judging fuel gas leak in a fuel cell system.
Accurate detection of fuel gas leak and judgment of the particulars thereof (hereinafter expressed simply as “judgment”) is absolutely essential in fuel cell systems. A technology in which a plurality of closed spaces are formed by shutoff valves or the like arranged in a fuel gas circulation supply line (hereinafter referred to also as a “fuel gas line”) comprising a fuel cell and in which the judgment of fuel gas leak is based on either pressure change (for example, speed of pressure) in this closed spaces or detection of the front-rear differential pressure of the shutoff valves or the like has been proposed (for example, see Japanese Unexamined Patent Application No. H8-329965) to satisfy this requirement.
However, there is a failing in the fuel gas leak judgment technology described above when the fuel cell system is restarted. That is to say, as a result of a phenomenon that occurs when the fuel cell system is stopped and then started again in which the nitrogen concentration in the fuel electrode side temporarily rises above the nitrogen concentration when the fuel cell is operating normally due to cross leak and the fuel gas leak decreases, the gas leak amount is sometimes underestimated.